On September 28, the Zhuhai Tunnel project saw new progress. After the north line of the subsea tunnel was holed through on July 17, the south line has now officially been holed through as well. With the dual-line holing-through of the subsea tunnel and the start of blasting construction on the Guadingjiao mountain tunnel, the overall project is expected to achieve full-line holing-through in 2025, with efforts to meet the conditions for opening to traffic by the end of 2025.

The Zhuhai Tunnel project alignment runs parallel to and south of the existing Zhuhai Bridge. It is designed as a dual-carriageway with three lanes in each direction and a design speed of 80 km/h, with a total length of about 5 km. The civil works are divided into two contract sections, TJ1 and TJ2. TJ1 starts from the east bank of the Zhuhai Bridge in the west, passes beneath the Guadingjiao mountain using the mining method, then turns north to connect to the main line of Zhuhai Avenue. TJ2 starts from the existing main line of Zhuhai Avenue in the west, turns south to pass beneath the newly built auxiliary road, then turns to the south side of the Zhuhai Bridge and enters the mid-river section of the Modaomen Waterway by shield tunneling, continuing eastward beneath the embankment, with a total length of 3.8 km.

The subsea tunnel section of the Zhuhai Tunnel project is one of the most challenging extra-large-diameter underwater shield tunnel projects in China. According to reports, the underwater shield tunnel works fall under the TJ2 contract section, constructed by China Railway Tunnel Group. This section is 3,800 meters long, including 2,930 meters of subsea shield tunnel and 870 meters of cut-and-cover section, with a maximum tunnel depth of 35 meters.

The project involves diverse construction methods and complex geological conditions, and is characterized as "large, difficult, risky, and innovative." "Large" refers to the 15.01-meter extra-large-diameter slurry shield machine; "difficult" refers to the shield working shaft reaching a depth of 30 meters and passing through more than 800 meters of composite strata with soft upper layers and hard lower layers, currently the longest bedrock section of an underwater shield tunnel project in China; "risky" refers to the shield passing close to and beneath numerous structures, with a complex environment and high construction risk; and "innovative" refers to the project's construction of an intelligent operation and maintenance health monitoring system for the tunnel, achieving full IoT coverage within the tunnel.

Because the shield alignment features long bedrock protrusions, high bedrock strength, large differences in hardness, and randomly distributed boulders that are difficult to detect, underwater shield tunneling is more difficult and risky, and underwater boulders and bedrock protrusion sections have become the greatest obstacle to safe and rapid shield construction.

To solve this problem, the project adopted two 15.01-meter extra-large-diameter slurry balance shield machines tailor-made for the unique silty clay strata of the Zhuhai area. Each shield machine is 123 meters long, weighs 4,200 tons, and has a cutterhead weighing 600 tons, with all technical indicators reaching world-leading levels. Among them, the "Kaituo" shield machine is responsible for tunneling the north line, and the "Fenjin" shield machine is responsible for tunneling the south line. They run parallel to and south of the Zhuhai Bridge, crossing the Modaomen Waterway estuary of the Pearl River from west to east.

During construction, there was another challenge: ensuring the safety of two water supply pipelines to Macao. According to the tunnel alignment design, both shield machines tunneling from west to east had to pass beneath two deeply buried water supply pipelines to Macao in the Guadingjiao section. The top of the shield machine was only 7.08 meters from the bottom of the water supply pipelines, and the soil structure around the pipelines lacked supporting capacity, with a 10-meter range before and after each pipeline constituting a risk impact zone.

To this end, during construction the project team adopted "fourfold" protective measures, including selecting precise tunneling parameters and cutters, conducting joint emergency drills across multiple departments and forming emergency support teams, establishing a multi-department liaison and coordination mechanism, and implementing a construction control system of "one-ring-one-assessment and one-ring-one-briefing." Ultimately, the two water supply pipelines to Macao achieved only "millimeter-level" settlement and remained "leak-free."